The present invention is a low voltage vacuum shorting switch, which is compact and rugged, and is particularly adapted for use in severe environments, such as in electrochemical processing plants.
Vacuum switches are well known in the art and generally comprise an insulating body through which movable contacts are sealed. At least one of the contacts or contact supports have some sort of flexible member between the contact and the sealed switch body to permit contact movement. A bellows-type shorting switch is detailed (in copending application Ser. No. 513,788, filed Nov. 10, 1974) in U.S. Pat. No. 3,950,628, issued Apr. 13, 1976, and owned by the assignee of the present invention.
Such low voltage switches are generally intended for use in electrochemical processing plants, such as chlorine plants. The low voltage switch is connected between high current carrying buses which supply current through a chemical solution. The buses pass through numerous chemical solution cells or tubs, and from time to time it is necessary to bypass a particular cell without interrupting the entire operation. The low voltage switch permits shorting out the bus at selected locations to permit maintenance operations.
It is important that opposed ends of the low voltage vacuum switch be easily connectable to the massive bus bars, with a large contact surface area to handle several thousand amperes of current. The typical electrochemical plant application means that the switch is used in a highly corrosive environment. The flexible member used to permit contact movement must be able to withstand this corrosive environment. The flexible member must permit the requisite axial movement of the contacts to permit bringing the contacts together to their shorted or closed position. The flexible member should also permit some flexibility at an angle to the axis to facilitate breaking the contacts apart when opening them, and also to facilitate mounting of the switch between the massive bus bars.
The present low voltage vacuum switch and operating mechanism combination is particularly useful in electrolytic chemical processing plants where large numbers of shorting switches are required for maintenance operations. These shorting switches are disposed between massive bus bars which connect chemical cells together, with the buses carrying thousands of amperes of current at low DC voltage levels. Periodic maintenance of the individual cells requires shorting the buses at the individual cell location. Such shorting assemblies are used with mercury cells for chlorine production or a variety of other electrolytic cells.
It has been the practice to use conventional knifeblade or exposed shorting contacts with the contacts being exposed to the corrosive chemical environment found in the vicinity of the cell. It is important that the shorting switch be located close to the cell to minimize resistance losses associated with long leads. It is also difficult to synchronize the mechanical closing of a group of shorting switches which may be in parallel groupings to handle the very large interrupting currents.